Could radiation dose in angiography procedures be reduced by simply using a larger display to view images? That's the suggestion of a prototype study published in the April edition of the American Journal of Roentgenology from a researcher at Johns Hopkins University.
Dr. Philippe Gailloud theorized that using the wide display mode on a 56-inch monitor could obviate the need for magnification during fluoroscopically guided interventional radiology procedures. Gailloud is co-director of the Johns Hopkins Pediatric Stroke and Neurovascular Center and director of the university's interventional neuroradiology unit.
In a phantom study, Gailloud found that viewing images on a larger display means that interventional radiologists do not have to use more radiation to zoom in on areas of interest -- enabling them to cut dose by half (AJR, Vol. 204:4, pp. W483-W485).
Radiation dose reduction
Heightened awareness of the dangers of medical radiation exposure has interventional radiologists looking for ways to drop dose. Well-known techniques for dose reduction include reducing the dose used per imaging frame, using variable or lower frame rates, limiting the number of angiography sequences acquired, and using collimation, among other tools. The use of magnification is another well-known but often overlooked tool for dose reduction, Gailloud believes.
The best option for reducing dose in single-plane angiography procedures would be to pick a low magnification factor with optimal collimation, he wrote. But this isn't optimal with standard monitors because anatomical structures being viewed would become too small to be seen by the operator.
Fortunately, large single-monitor displays have recently been introduced for use in angiography suites. The monitors are customizable: For example, in the standard setting they can be configured with six small equal-sized images showing different aspects of the interventional procedure, while a wide display mode could be used to show a single large image and two smaller images. In theory, the size of the large image would be big enough to enable it to be viewed without magnification -- and its radiation boost.
Gailloud tested the hypothesis using a standard abdominal and pelvic phantom that was imaged with a biplane angiography system (Artis zee, Siemens Healthcare) equipped with a 56-inch display capable of standard and wide display settings. He used a 10-second fixed subtracted radiographic sequence at a variable frame rate setting, with and without collimation, and repeated the imaging sequence at a variety of different zoom levels. Fluoroscopy was not performed in the experiment.
Radiation dose for each acquisition at the different zoom levels was calculated at the air kerma in milligrays by recording the report that was automatically generated by the angiography system. Gailloud then measured the size of the acquired images as they appeared on the display by measuring the length of a 1-cm gradation of a ruler that had been placed next to the phantoms; this allowed him to calculate the change in image size at the various zoom levels.
As expected, Gailloud found that radiation increased significantly with each increase in magnification. But displaying the image on a wide-format monitor enabled the same-sized image to be viewed with a lower zoom level and lower radiation dose. For example, an image displayed at zoom level 3 on a standard display setting was the same size and quality as zoom level 1 with a wide display setting -- with the latter technique conferring a 50% to 60% dose reduction depending on whether collimation is used.
Gailloud suggested that hospitals using multiple smaller monitors in their angiography suites consider switching to newer large monitors that support wide-display settings.
"Centers that have multiple angiography suites with different types of monitors should try adapting their daily schedule to get optimal radiation reduction benefits -- for example, by prioritizing the use of suites equipped with a large display for single-plane procedures," Gailloud wrote.
